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<html lang="en">

<head>
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    <title>Document</title>
    <style>

    </style>
</head>
<button>点击</button>
<div></div>
<body>
    
    <script>
     var btn = document.querySelector('button')
     var div = document.querySelector('div')
     btn.addEventListener('click',function() {
        location.href = 'http://www.itcast.cn';
     })
     var timer = 5;
     countDown();
     setInterval(countDown, 1000);
      function countDown() {
        if(timer == 0){
            location.href = 'http://www.itcast.cn';
        } else{
            div.innerHTML = '将在' + timer + '秒钟后跳转到首页';
            timer--;
        }
     }
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</body>

</html>